The long-term goal of this research is to better understand MHC class II-restricted antigen presentation. Class II a/beta heterodimers associate intracellularly with a third polypeptide chain, the invariant chain, that affects class II maturation. A significant contribution by this lab during the past period of support was the generation of a novel mouse strain carrying a targeted mutation at the invariant chain locus and the description of its striking phenotype. Experiments proposed in this application aim to further analyze the ability of invariant chain to affect the structure of MHC class II molecules on the surface of diverse antigen-presenting cells in the intact animal. We plan to compare the invariant chain dependency of class II molecules produced in different MHC backgrounds and to evaluate possible effect(s) of IL4/LPS stimulation on class II maturation. We will also examine biosynthesis and maturation of class II molecules expressed by dendritic cells, activated macrophages, and thymic stromal cells. A second goal is to further analyze the contribution of MHC-associated Ii chain to CD4+ T cell maturation. We plan to test the possibility that the few remaining CD4 T cells present in Ii mice may represent an intermediate, partially selected CD4 subset. We will examine their V/beta repertoire, and determine if these cells are triggered to proliferate and/or produce lymphokines in response to TCR crosslinking. Additionally, thymic organ cultures will be used to study defective CD4+ T cell maturation. We will seek evidence for positive selection by peptide and evaluate the V/beta repertoire of emerging CD4+ T cell clones. Finally, a major goal is to examine potentially divergent role(s) played by structurally distinct Ii31 and 41 proteins that arise as the result of alternative mRNA splicing. We plan to generate transgenic mouse strains that exclusively express the p31 or p41 form of invariant chain protein that also show an appropriate tissue-specific pattern of expression in vivo. These novel mouse strains will be used to analyze the capacity of invariant chain p31 and/or p41 alone to affect class II biochemistry, APC activity, and T cell selection in these strains. Overall, these experiments will hopefully provide further insight into functional role(s) played by the MHC class II-associated Ii chain in immune regulation.